To use those 5MM machine screws, you'll need to widen the 8 screw holes in the metal case that previously secured the X-clamp posts. They are highlighted in the second photo.
To widen them, use a 3/16 inch drill bit with a drill press or hand drill. If you're using a hand drill, set a wooden block under each hole as you drill it to avoid warping the case. If you're using a drill press as I did there should be a steel pedestal with a hole for the drill bit to pass through, saving the case from serious FUBAR-age.
Have the bit spinning before you push into the center of the hole. Repeat this for all the holes. Make sure there are no burrs left on the holes or shards kicking around in the case afterwards. Bang it around a few times to get them out. The last thing you'd want is to have your 360 die from little pieces of metal shorting it out.